(1) Field of the Invention
The present invention relates to through type capacitors incorporated into various electric and electronic appliances.
(2) Description of the Prior Art
Conventionally, through type capacitors employ a dielectric element formed of a ceramic and having a cylindrical shape or a dielectric element formed of a plastic film rolled into a cylindrical shape.
FIGS. 1 (a) and (b) show sections of known through type capacitors comprising a ceramic and a plastic film acting as the dielectric element, respectively.
The through type capacitor 31 shown in FIG. 1 (b) is designed for low voltage use. This capacitor 31 includes a cylindrical ceramic 30, electrodes 32 and 33 formed on an inner and an outer surfaces of the ceramic 30, and a through conductor 34 connected to the inner electrode 32.
FIG. 1 (a) is a partly sectional view of a through type capacitor 21 designed for high voltage use and comprising plastic films acting as the dielectric element. This through type capacitor 21 includes a cylindrical capacitor unit 22, a through terminal 23, an earthing terminal plate 24, a collector plate 25, and a cylindrical insulator 28.
The capacitor unit 22 includes a first tape-shaped dielectric film 222 with electrode layers 221 formed on a main surface thereof, and a second tape-shaped dielectric film 224 having substantially the same width as the first dielectric film 222 and having electrode layers 223 formed on a main surface thereof. The first and second dielectric films 222 and 224 are wound into a cylindrical shape around the insulator 28 with the electrode layers 223 of the second dielectric film 224 superposed on another main surface of the first dielectric film 222.
The electrode layers 221 formed on the first dielectric film 222 extend from one side of the first dielectric film 222, leaving a fixed margin, to the other side thereof and onto one end face of the capacitor unit 22. The electrode layers 223 formed on the second dielectric film 224 extend from the side of the second dielectric film 224 corresponding to said other side of the first dielectric film 222, leaving a fixed margin, to the side thereof corresponding to said one side of the first dielectric film 222 and onto the other end face of the capacitor unit 22.
Metallicon electrodes 26 and 27 are formed by applying a molten metal to the two end faces of the capacitor unit 22. The metallicon electrode 26 is electrically connected to the electrode layers 221 of the first dielectric film 222 and the other metallicon electrode 27 to the electrode layers 223 of the second dielectric film 224.
The earthing terminal plate 24 and the collector plate 25 are soldered to the metallicon electrodes 26 and 27, respectively.
The through type capacitor 31 employing a ceramic as illustrated in FIG. 1 (b) undergoes great capacity variations due to temperature variations. Its capacity shows a sharp drop to -30.about.-80% with a rated voltage application. In addition, it is difficult for this type of through type capacitor to have a large capacity and impossible to avoid high impedance particularly in low frequency ranges. If this through type capacitor is enlarged for high voltage use, its manufacturing cost becomes considerably high. There is also a problem that the weight of the ceramic makes it difficult to realize a light and small through type capacitor.
The through type capacitor 21 employing plastic films as the dielectric element as illustrated in FIG. 1 (a) involves winding of the two dielectric films, which poses the problem of very low productivity.